As disclosed in U.S. Pat. No. 4,293,915, issued Oct. 6, 1981, entitled "Programmable Electronic Real-Time Load Controller", Carpenter et al., and assigned to the assignee of the present invention, a programmable electronic real-time load controller includes: a plurality of load control circuits, each being adapted to be interconnected with an electrical load circuit or "load"; a hardware clock; and, a programmed data processor for responding to real-time information from the hardware clock to effect control of the energization state of each load in accordance with a time schedule that has been entered by a user into the data processor. The user is permitted to flexibly program the time schedule by selecting, in advance, a number of control events and associated event times for each of the plurality of loads and for each day in a week. Each selected control event either causes the load to be turned on, to be turned off, or to be duty-cycled, from a time in real-time corresponding to the associated event time to a time in real-time corresponding to a subsequent event time. Accordingly, the "on time" of each load is conformed to the periods during which energization of the load is required so as to limit energy consumption at the facility at which the loads are located.
Other electrical load control systems, sometimes referred to as power demand monitoring and limiting systems, continuously measure and compare the actual rate of power being consumed by a plurality of loads at a facility with a predetermined rate of power consumption, sometimes referred to as a set point. If the actual rate exceeds the set point, then one or more of the loads are turned off to decrease the actual rate of power consumption. If the converse exists, then one or more of the loads are turned on to increase the actual rate of power consumption.
The preferred application for such power demand monitoring and limiting systems lies in the regulation of power consumption by electrical utility customers. As is well known, the charge made to each utility customer by the utility is dependent not only on the total energy consumption over a substantial period of time, such as a month, but also on whether or not the total energy consumption over any of a succession of shorter time periods, referred to as demand intervals, has exceeded a maximum energy demand established by the utility.
When used in such applications, the power demand monitoring and limiting systems may include a power monitoring and regulating circuit which produces an analog signal representing the actual rate of power being consumed. The analog signal is compared within the power monitoring and regulating circuit with a reference signal representing the set point. When the analog signal exceeds or is less than the reference signal, the power monitoring and regulating circuit functions to produce output signals for effecting load control. An example of such a power monitoring and regulating circuit can be seen in U.S. Pat. No. 4,034,233, entitled "Power Monitoring and Regulating Circuit and Method Having an Analog Input Representing Power Rate and Digital Output for Controlling the On/Off States of a Plurality of Loads", Leyde, issued July 5, 1977 to the assignee of the present invention.
The output signals from the power monitoring and regulating circuit are supplied to a load control circuit that is adapted to control the on/off states of the loads. As an example, the output signals may be in the form of one or more shed pulses that direct the load control circuit to shed a load for each shed pulse, with the number of shed pulses being related to the amount by which the actual rate of power consumption exceeds the set point. Similarly, when the actual rate of power consumption is less than the set point, one or more add pulses are produced, each such add pulse directing the load control circuit to add one load. The load control circuit may include provisions for determining the sequence in which the plurality of loads at the facility are to be added or shed in accordance with the add and shed pulses from the power monitoring and regulating circuit. For example, a priority sequence may be established in which certain essential loads, such as air conditioning equipment or the like, are shed only after other loads, such as lighting, have been shed, and in which such essential loads are added before such other loads are added. Provision may also be made for adding and shedding certain loads in a variable, rotating order in response to the add and shed pulses. Examples of such load control circuits may be seen in U.S. Pat. No. 4,031,406, entitled "Method and Apparatus for Controlling Electrical Loads", Leyde et al., issued June 21, 1977 to the assignee of the present invention, and U.S. Pat. No. 4,064,485, entitled "Digital Load Control Circuit and Method for Power Monitoring and Limiting System", Leyde, issued Dec. 20, 1977 to the assignee of the present invention.
Heretofore, such power demand monitoring and limiting systems have not included any provision for real-time control of the loads associated therewith, e.g., that in which the loads are turned on, turned off, or duty-cycled in real-time in accordance with a time schedule. Conversely, the programmable electronic real-time load controllers have not included any provision for demand limit control, e.g., that in which the loads are turned on or turned off in order to maintain total energy consumption over each demand interval below the maximum energy demand established by the utility. As a result, the use of a power demand monitoring and limiting system will not permit the user to conform the "on time" of each load to that for which energization of the load is required, and the use of a programmable electronic real-time load controller may result in the maximum energy demand being exceeded.
It is therefore an object of this invention to provide an apparatus that permits demand limit control to be provided by a programmable electronic real-time load controller.
It is another object of this invention to provide such an apparatus which functions to provide demand limit control that is coordinated with the real-time control provided by the programmable electronic real-time load controller.
It is yet another object of this invention to provide such an apparatus which allows the user to select or de-select any given load for demand limit control.
It is still another object of this invention to provide such an apparatus whose implementation of demand limit control can be enabled or disabled in response to an external device, or, at predetermined times established by the programmable electronic real-time load controller.
It is a further object of this invention to provide such an apparatus which permits the controller to maintain any load selected for demand limit control either on or off for predetermined, minimum times so as to avoid excessive on-off cycling of the load.
It is yet a further object of this invention to provide such an apparatus which permits the controller to rotate the off states of those loads selected for demand limit control so as to minimize the maximum off time of any such load.
It is still a further object of this invention to provide such an apparatus which permits the controller to rotate the on/off states of loads selected for demand limit control in a predetermined order.
It is still a further object of this invention to provide such an apparatus which can be implemented in an easy and inexpensive manner by the use of readily available, integrated circuit, microprocessor components which are compatible with and which function under control of the data processor within the programmable electronic real-time load controller.